Understanding Glyphosate Acid Equivalents

Like most herbicides, costs have gone up from years past and product availability can, at times, play a major factor in determining the price. When supplies are limited, producers must often consider using different formulations of the products they are used to purchasing. The herbicide glyphosate is no exception as it is one of the most popular and widely used herbicides in U.S. wheat production. Producers like it for its ability to control a broad spectrum of weeds while leaving no soil residual.

Several different salt formulations of glyphosate are manufactured. These different formulations of glyphosate include Diammonium Salt, which can be found in the product Drexal Imitator DA; Dimethylammonium Salt, which can be found in products such as Duramax Herbicide; Isopropylamine Salt, which is found in products such as Roundup Pro, Gly-Star Plus, Mad Dog 5.4 and others; and Potassium Salt, which is used in Roundup Original Max, RT3, PowerMax and others.Product labels such as RT3 will provide a range of rates (in fluid ounces per acre) for controlling various weeds. But does this mean that the same rate used for one glyphosate product will be equivalent to the rate used in other glyphosate formulations? The answer is No.

Glyphosate is a weak acid. When the glyphosate salt is absorbed by plants, the salt is disassociated at the site of action, and it is the glyphosate acid that binds to the target enzyme resulting in herbicidal activity. The amount of glyphosate acid varies depending on which salt formulation, also known as the active ingredient or ai, your product uses. Thus, the application rate that you are used to using may be different for a different formulation or salt of glyphosate.

It is recommended when comparing glyphosate products, such as those listed above, to look at the amount of “acid equivalent or ae” rather than the amount of “active ingredient” that is listed on the label. This information will be found listed below the percentages of Active and Other Ingredients on the pesticide label, see RT 3 label below.

Figure 1. RT3 ingredient statement.

Here it states this product:

“Contains 660 grams per liter or 5.5 pounds per U.S. gallon of the active ingredient glyphosate, in the form of its potassium salt. Equivalent to 540 grams per liter or 4.5 pounds per U.S. gallon of the acid, glyphosate.”

Trade Name	Salt Formulation	Pounds per gallon AI (formulated as the salt)	Pounds per gallon acid equivalent	Rate (in fl oz) to equal 1 lb acid equivalent
Drexal Imitator DA	DIAMMONIUM SALT	3.6	3	42.6
Duramax Herbicide	DIMETHYLAMMONIUM SALT	5.07	4	32
Gly-Star	ISOPROPLAMINE SALT	4	3	42.6
RT3	POTASSIUM SALT	5.5	4.5	28.4

Table 1. Amount of the active ingredient and the acid equivalent found in RT3 and other glyphosate products.

Table 1 compares different glyphosate products and the number of pounds per gallon of active ingredients along with the pounds per gallon acid equivalent. The rate (in fluid ounces) to equal 1 pound (lb) acid equivalent column was calculated by taking the number of ounces in 1 gallon (128) and dividing it by the pounds per gallon acid equivalent. So, if a producer has been using RT3 and then switches to Gly-Star because of availability and/or cost, the application rate will need to be increased to deliver the same amount of glyphosate acid to achieve the equivalent effect.